The invention relates to a process for controlling the drive of a reel of a continuous web of material, preferably a web of packaging material, from which blanks are successively severed and fed to a processing machine s especially a packaging machine or a folding unit (folding turret) thereof, said web of material forming a material reservoir.
The invention further relates to an apparatus for feeding a web of material to a processing machine, said apparatus having a motor for driving a reel of the web of material to unwind the latter off the reel and having a (web of) material reservoir, through which the (wound off) web of material can be conveyed, in particular for conducting said process.
In the abovesaid apparatus or process, the feeding of the web of material to the processing machine can be problematic, since the processing machine, especially a packaging machine, is usually run at different operating states which often and quickly alternate with one another. Different operating states of the machine may be for instance standstill, normal operation, (short-time) overspeed operation or (short-time) crawling speed.
In spite of these alternating operating states of the processing machine, the latter still has to be sufficiently supplied with material in each of the operating states. In principle, a sufficient supply of material can be ensured by providing a material reservoir as a buffer between the reel and the processing machine. Depending on the holding capacity of the material reservoir, the reel can react to the momentary requirement of the machine with a certain delay and (re)fill the material reservoir as required.
Nevertheless, even with a material reservoir being provided, the reel still has to follow the operating states of the downstream machine, although possibly with a delay.
This is particularly problematic, if the reel is heavy and needs relatively large accelerations for changing the operating states. The heavy reel has an inertia of masses which makes a direct reaction to the requirements of the machine or the operating states difficult or impossible even if such reaction is delayed.
Heavy reels are particularly used in connection with packaging machines, if for instance packaging material of thin cardboard is to be made into packs. With such packaging processes, it is known in the packaging art to divide the web of material into pack blanks, the individual blanks remaining connected to one another via residual web connections so that they can still be held ready as a web of material on a reel. The blanks are severed from the web of material, for instance by being torn or sheared off, only when they are in the region of the packaging machine. Regarding this state of the art, reference is made to DE-OS 37 16 897, DE-OS 37 35 674 and DE-OS 37 35 675.
In order to bypass or avoid the afore-described problem, caused by the relatively high dead weight of the reel which is to be driven, it is desirable to drive the reel as independently as possible from the operating states of the downstream machine and thus as continuously as possible.